Electric ignition systems



1959 F. R. F. RAMSAY 2,909,575

ELECTRIC IGNITION SYSTEMS Filed Sept. 4, 1956 I FIG. 8,

INVENTOR FRANK RF. Rams BY 406%, 4 4, M

Papa/a4 ATTORNEYS ELECTRIC IQNITION SYSTEMS Frank Raymond Faber Ramsay,East Sheen, London,

England, assignor to D. Napier & Son Limited, London, England, a companyof Great Britain Application September 4, 1956, Serial No. 607,726

Claims priority, application Great Britain September 5, 1955 Claims.(Cl. 315-209) This invention relates to electric ignition systems foruse with low resistance sparking plugs, that is to say, sparking plugshaving a resistance of the order of a few hundred to a few thousand ohmsand requiring a potential of only a few hundred to a few thousand voltsto fire them.

Sparking plugs of the air gap type have a very high resistance andrequire an ignition system capable of producing a potential of the orderof tens of thousands of volts to fire them. This potential is normallyobtained from the secondary winding of a magneto or ignition coil, whichhas a very large number of turns and is of high impedance.

Sparking plugs of another kind, known as surface discharge plugs, havealso been developed. In such plugs the gap between the electrodes isbridged by a poorly conducting solid substance, and when a potential isapplied between the electrodes a current leaks across the surface of thebridge on one or more paths. The temperature along these paths growsrapidly to the point where the gas adjacent to them becomes ionized andpermits an arc ot strike. The resistance of such plugs has usually beensuch that a potential of about 2000 volts is required to fire them.Ignition systems for use with such plugs have usually employed a largecharged condenser as the source of potential, practically all of theenergy for the discharge being stored in this condenser. Severaldifferent ignition systems of the kind have been devised. Such ignitionsystems have, in general, included a vibrator-operated step-uptransformer fed from a source of direct current such as a battery, thesecondary winding of the transformer charging the large condenserthrough a rectifier, and means such as a series spark gap for connectingthe large condenser, when charged, to the plug.

Recently, surface discharge plugs of low resistance, as defined above,have become available, and ignition systems similar to those used withthe higher resistance surface discharge plugs but modified to produce alower potential have been employed.

It is an object of this invention to provide an electric ignition systemsuitable for use with such low resistance sparking plugs which does notrequire a large condenser (i.e. a condenser large enough to storevirtually all the spark energy), nor a high voltage step-up secondarywinding, nor a rectifier, nor a series spark gap.

Other and further objects will be apparent to those skilled in the artfrom the following disclosure.

These objects are achieved according to the present invention, by anelectric ignition system in which both the ionizing potential and themain spark energy are produced by the collapse of flux in an inductiveWinding of low impedance (i.e. an inductive winding whose number ofturns and impedance are only a small fraction of those of the secondarywinding of an ignition system for an air gap sparking plug), a condenseris connected across the plug to permit the establishment of anionization path through the gas for the discharge of the main sparkenergy from the inductive winding, and the flux is built up be-2,900,575 Patented Aug. 18, 1959 2 tween discharges by a chargingcircuit comprising an inductive winding connected across a source ofdirect current through a contact-breaker actuated by an oscillatingsprung balanced mass of a natural periodicity of not more than abouttwenty oscillations per second. a

The invention may be performed in various ways and one particular formof ignition system embodying the invention, and some modifications, Willbe described by way of example with reference to the accompanyingdrawings, in which: j a

Figure 1 is a side view of the inductive system and the oscillating massassembly, shown partly in section,

Figure 2 is a cross-sectional view taken on the line IIII in Figure 1,

Figure 3 is a diagram of a simple form of circuit incorporating theinductive system shown in Figures 1 and 2; and

Figures 4 to 8 are diagrams of alternative forms of circuit.

The ignition system shown in Figures 1 to 3 of the drawings comprises aninductive winding 10 consisting of a large number of turns of relativelyheavy gauge copper Wire wound round one limb of a laminated iron core11, this core forming a closed circuit except for a narrow gap 12. Sinceit is desirable for the ohmic resistance'of the winding 10 to be as lowas possible the ratio of weight of copper in the winding to weight ofiron in the core 11 will generally be much higher than is usual innormal transformer practice. Mounted on the core 11 is a frame 13carrying an oscillating mass 14 and a contact-breaker comprising amovable contact 15 and a stationary contact 16. The contacts areconnected in series with the inductive-winding 10, to connect it to asource of direct current (e.g. a battery), indicated by positive andnegative terminals in the drawing, when the contacts are closed.

The oscillating mass 14 comprises a cylindrical body 17 which is mountedon a bearing member 18 which is rigidly fixed to the frame 13. Thecylindrical mass 17 is free to rotate on the bearing member 18 but isconstrained by alight spiral spring 19 towards a central position inwhich the spring is unstressed. The cylindrical mass 17 is balancedabout its axis of rotation. It is made largely of non-magnetic materialsuch as brass but is provided with a segmental insert 20 of magneticmate rial such as soft iron adapted to be attracted towards the limb 21of the iron core 11 by stray magnetic flux when the winding 10 isenergized. This attraction imparts an unbalanced force to the mass tomaintain it in oscillation. As the mass swings in the counter clockwisedirection as seen in Figure 1 through the center of its amplitude ofoscillation, i.e. when it is moving with its maximum velocity, a hammer2.2 which it carries strikes a light leaf spring 23 carryng the movablecontact 15 and separates the contacts as shown in dotted lines inFigure 1. This disconnects the inductive winding 10 from the directcurrent supply and causes the flux to collapse. One efiect of thecollapse of flux is that the magnetic attraction on the ion segment 20of the mass 14 ceases, thereby permitting the spring 19 to cause themass to swing back in the clockwise direction. As the mass swings backthrough the centre of its amplitude of oscillation the contacts closeagain, so that the inductive winding 10 is again connected to the sourceof direct current and the flux builds up again.

When the contacts 15 and 16 separate and the flux in the inductivesystem collapses, a potential is produced across the inductive winding10 which is applied across a condenser 24 (Figure 3) and across a lowresistance surface discharge sparking plug 25. Although the condenser 24limits the peak potential to a voltage of some hundreds of volts this issufficient to initiate ionisation of the sparking plug, and the collapseof flux is retarded sufficiently to ensure that the ionisation iseffective to produce an adequate low resistance gas path between theplug electrodes through which a spark can jump. Energy is thustransferred from themagnetic field of the inductive winding to the plug25. As the collapse of flux proceeds, the potential across the inductivewinding and across the plug decreases, but the spark continues to passuntil'the magnetic field of the inductive winding 10 has practicallycompletely collapsed.

Too 'low an initial rate of discharge due to having too small acondenser 24 would result in the flux dying away before the resultantenergy could discharge across the sparking plug 25. Conversely, toolarge a condenser 24 would lower the initial voltage below thatnecessary for ionisation, and no spark would result. This would be thecase with a condenser large enough to store a substantial portion of thetotal energy, as in certain prior art proposals. As an example, in aparticularcase, a condenser of 2 'microfarads is used in conjunctionwith an inductive winding providing a spark with an energy of about 4joules. If the same inductive winding and circuit were used in aconventional manner, storing practically all the energy in the condenserbefore ionisation, a condenser of about 40 microfarads would berequired.

The condenser 24, being connected across the contacts and 16, alsoserves to suppress arcing at the contacts.

The moment of inertia of the mass 14 and the charaeteristic of thespring 19 are so chosen that the natural periodicity of oscillation isnot more than about twenty oscillations per second, for instance aboutfive oscillations per second. If the flow of direct current through theinductive winding 10 were interrupted at a higher frequency, thesparking rate at the plug 25 would be such that the heat generated wouldfuse the surface discharge material and ruin the plug. Moreover, arelatively low frequency of oscillation gives sufficient time for anample build-up of flux to take place in the periods when the contacts 15and 16 are closed, so that adequate energy is available for producingfat sparks.

Since the spring 19 controlling the mass must be relatively light inorder that the natural periodicity of the oscillating sprung mass 14shall be low, the mass would be affected by linear accelerations and bychanges in attitude of the apparatus unless the mass were balanced aboutits centre of oscillation. It will be apparent to those skilled in theart, however, that the mass 14 need not necessarily be of cylindricalform. For instance it could be made in the form of a lever balancedabout its fulcrum. It will also be apparent that the magnetic field formaintaining the oscillations need not necessarily be the stray flux fromthe iron core 11 adjacent the gap 12, since a separate electromagnetcould be used for this purpose, connected either in series or parallelwith the said inductive winding 10.

In the circuit shown in Figure 3 the current surge produced by thecollapse of flux in the inductive winding 10 passes through the battery.Also, if by some mischance the sparking plug 25 should beshort-circuited, the inductive winding 10 will remain in series with thebattery and the short circuit current will not flow through the contacts15 and 16.

Another form of circuit is shown in Figure 4. In this circuit thepositions of the inductive winding 10 and of the contacts 15 and 16 arein effect reversed from the positions they occupy in the circuit shownin Figure 3, and when the plug 25 has been ionized the surge of currentfrom the inductive winding 10 passes directly to the plug withoutpassing through the battery. In this circuit the condenser 24 is notconnected across the contacts 15 and 16, so a separate arc-suppressingcondenser 26 is provided.

In certain cases the voltage of the available direct current sourcemight be such that if the values of capacitance and inductance of thesystem remained unchanged the potential produced across the inductivewinding would be either too high or too low for the particular sparkingplug. One way of getting over this difficulty is by arranging theinductive winding as an auto-transformer. Two different arrangements ofthis kind are shown in Figures 5 and 6.

In Figure 5 the inductive winding 27 has a tapping 28 to which themovable contact 15 is connected. In this arrangement the inductivewinding 27 acts as a voltage step-up auto-transformer, since thepotential applied across the condenser 24 and the sparking plug 25 willbe developed by a larger number of turns than are connected across thesource of direct current when the contacts are closed.

In Figure 6 the inductive winding 29 is in the form of a voltagestep-down auto-transformer. In this case a tapping 39 is connected tothe condenser 24 and the sparking Plug 25. V

Instead of arranging the inductive winding as an autotransformer, atransformer having separate primary and secondary windings 31 and 32respectively could be employed, as shown in Figure 7, the numbers ofturns in both windings being selected to suit requirements.

In order to prolong the spark if this is desired, for instance forigniting a heavy fuel oil or solid powdered fuel, an inductanceconnected in series with the sparking plug beyond the connection to thecondenser 24 may be provided. One such arrangement is shown in Figure 8,in which a series connected inductance 33 is formed by a few additionalturns on the inductive winding 34 beyond the tapping 35 which leads tothe condenser 24.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electric ignition system for use with a sparking plug having lowresistance of a few hundred to a few thousand ohms comprising aninductive winding whose number of turns and impedance are only afraction of those of the secondary winding of an ignition system for anair gap sparking plug, a charging circuit for said inductive windingincluding a source of direct current and a contact breaker, anoscillating spring balanced mass having a natural periodicity of notmore than about twenty oscillations per second adapted to actuate saidcontact breaker to close said charging circuit to build up flux in saidinductive winding and to interrupt said charging circuit to cause saidflux to collapse, a condenser, connections permanently connecting saidcondenser across said sparking plug, and connections permanentlyconnecting said inductive winding across said sparking plug wherebyenergy released by each collapse of flux in said inductive winding firstionizes said sparking plug and then provides a spark discharge acrosssaid ionized sparking plug.

2. An electric ignition system according to claim 1 which includeselectromagnetic means for maintaining said mass in oscillation.

3. An electric ignition system according to claim 2 in which saidelectromagnetic means comprises stray flux from said inductive winding.

4. An electric ignition system according to claim 2 in which said massis made mainly of non-magnetic material and has a part made of magneticmaterial disposed eccentn'cally with respect to the axis of oscillation.

5. An electric ignition system according to claim 1 in which said massis disposed in a partial relationship to said contact breaker such thatsaid contact breaker is actuated by said mass when said mass is in thevicinity of the centre of its amplitude of oscillation.

6. An electric ignition system according to claim 5 in which saidcontact breaker comprises a fixed contact, a movable contact and aflexible carrier for said movable contact, and said mass is adapted tostrike said flexible carrier to separate said contacts.

7. An electric ignition system according to claim 1 in which saidconnections between said inductive winding and said sparking pluginclude at least a part of another inductive winding.

8. An electric ignition system according to claim 7 in which said otherinductive winding is separate from said first mentioned inductivewinding and the two windings are coupled by a common iron core.

9. An electric ignition system which said inductive winding is in theform of an auto transformer with difierent numbers of turns connected inthe charging circuit and to the sparking plug respectively.

10. An electric ignition system according to claim 7 in which said otherinductive winding is connected in series with said first mentionedinductive winding between said sparking plug and one of said connectionsto said condenser.

according to claim 7 in 5 References Cited in the file of this patentUNITED STATES PATENTS Apple June 6, Falge et a1. May 12, Lodge May 11,Ruben Nov. 27, Kasarjian Feb. 4, Ramsay May 17, Debenharn May 1,

